This invention relates to improved seals between relatively rotating members in boring apparatus such as that shown, e.g., in Peterson U.S. Pat. Nos. 3,897,837 and 3,945,447, the disclosures of which are hereby incorporated by reference as background information.
The boring apparatus shown in the Peterson patents employs lubricated bearings for cutters mounted to rotate on internal, non-rotating shafts. Seals are required to retain the lubricant and exclude dirt and abrasive material. Under heavy radial loading (e.g., when enlarging a hole in rock), the cutter shafts (which have high length-to-diameter ratios of about 4:1 or more between supports) deflect elastically. To avoid excessive pressures near the ends of the journal bearings it is necessary to use "soft" bearings which can accommodate the shaft deflection. As a result, there can be considerable radial motion between the cutters and their shafts during operation. Furthermore, normal fabrication tolerances (e.g., 0.010"-0.067" inch) inherently permit appreciable relative axial motion between the cutters and their shafts in response to the reversing axial loading experienced during operation. The bearing seals must permit these radial and axial motions (in addition to the basic rotational motion between the cutters and their shafts) while being subjected to an extremely dirty and abrasive environment.
Similar requirements are imposed on other sorts of rotary rock drills, and would also apply to roller stabilizers if used with sealed, lubricated bearings.
The above sealing requirements must be met even though relatively little space is available for seals on these reamers and stabilizers.